1. Field of the Invention
The present invention relates to a vehicle body frame structure for a two-wheeler.
2. Description of Background Art
In the related art, a vehicle body frame structure for a two-wheeler is known wherein an exhaust pipe, provided at the front of an engine, is located in the vicinity of the vehicle body frame. See, for example, Japanese Patent No. 3,370,888.
Referring now to FIG. 15 attached hereto which corresponds to FIG. 1 in Japanese Patent No. 3,370,888 the following description is provided. Note, that the latter half of the drawing is omitted, and the components are renumbered.
FIG. 15 is a side view of a vehicle body frame structure for a two-wheeler in the related art, showing a pair of left and right down pipes 302, 302 (only the reference numeral 302 designating the nearer one is shown in the drawing) extending substantially downwardly from the head pipe 301 and provided at the front end of the vehicle body frame. A plurality of exhaust pipes 304 extend downwardly from the front of an internal combustion engine 303 so as to curve therefrom. A front wheel 306 is mounted to the head pipe 301 via a front fork 307.
The above-described down pipe 302 requires a great rigidity for supporting the weight of the internal combustion engine 303 and suppressing vibrations of the internal combustion engine 303. Thus, a structure of connecting the left and right down pipes 302, 302 with a cross pipe is employed. When the left and right down pipes 302, 302 are connected with the cross pipe, it is necessary to pay attention to interference between the cross pipe and the exhaust pipes 304. When an attempt is made to secure a clearance between the cross pipe and the exhaust pipes 304 disposed in front of the cross pipe, the distance between the exhaust pipes 304 and the front wheel 306 is reduced.
In addition, for example, it is difficult to dispose a heat-discharging member such as a radiator, an oil cooler, or other auxiliary components between the front wheel 306 and the exhaust pipes 304. More specifically, a large sized auxiliary component cannot be disposed therebetween. In particular, in the case of the internal combustion engine 303 having an in-line four-cylinder engine and thus requiring a large lateral width, since the distance between the left and right down pipes 302, 302 increases, a greater rigidity is required. However, since it is also necessary to take the interference with the plurality of exhaust pipes 304 into consideration, the vehicle body frame and the exhaust pipes 304 are further restrained in flexibility in design relating to their shapes and locations.
A vehicle body frame structure for a two-wheeler employing pipe members is known. For example, see Japanese Patent No. 3194288 (P. 2–3, FIG. 1)
Referring to FIG. 28 shown below which corresponds to FIG. 1 of Japanese Patent No. 3194288 will be described. The components are renumbered.
FIG. 28 is a perspective view showing a vehicle body frame structure for a two-wheel vehicle in the related art, showing that a vehicle body frame 1300 includes a pair of left and right top tubes 1302, 1302 extending rearward from a head pipe 1301 and curving downward, and a pair of left and right down tubes 1304, 1304 extend downwardly from the head pipe 1301 and curve rearward.
The down tubes 1304 are formed of a round pipe member.
In a two-wheeler, one of the portions which limits an angle of inclination of the vehicle body, that is, a bank angle, is the above-described down tubes 1304 which are located at the lower portion of the vehicle body.
Therefore, for example, the positions of the down tubes 1304, 1304 may be moved upwardly or inwardly as a considerable countermeasure. However, since there is an engine inside the vehicle body frame 1300, the above-described movement is difficult. Though it is also possible to eliminate the down tubes 1304, the strength of the vehicle body frame will decrease.